Beyond the CBC and Reticulocyte Count: Early Detection of Iron Deficiency Anemia

In my May 2018 post (Not your Grandmother’s Hematology), I discussed the history of hematology and chronicled how far we have come in the last 60 years. We have progressed from manual counting of cells to the first Coulter Counter in 1956, which revolutionized hematology by being able to automate the counting of red blood cells, to modern instruments that can report up to 30 parameters and perform up to 400 CBCs an hour. Among these parameters are what are termed advanced clinical parameters, new parameters which provide physicians with additional information about the state of blood cells. In this blog I will explore how one of these advanced clinical parameters, the Reticulocyte Hemoglobin content, can provide physicians with information that can assist them with earlier detection, differential diagnosis and better management of iron deficiency and iron deficiency anemia.

Case Study

A 29 year old female was seen by her gynecologist reporting a history of heavy menstrual bleeding with current bleeding lasting 15 days. The doctor discussed various treatment options with the patient and a CBC was performed. CBC results are shown below.

Test

Result

Flags

Reference

WBC

7.23

4.5-10.5 K/CMM

RBC

4.38

3.70-5.30 M/CMM

HGB

12.0

12.0-15.5 GM/DL

HCT

36.2

36.0-46.0 %

MCV

82.6

80-100 FL

MCH

27.4

27.0-34.0 PG

MCHC

33.1

32.0-36.0 %

PLT

243

150-450 K/CMM

MPV

11.0

9.6-12.0 FL

RDW

12.5

0-15.1 %

This CBC shows no abnormal flags. Based on patient history and presentation, the physician questioned iron deficiency despite normal hemoglobin and hematocrit, MCV and MCHC. He ordered a reticulocyte profile on the same specimen with the following results:

Test

Result

Flags

Reference Range

Retic

1.55

0.5-2.0 %

Abs Retic

0.0679

H

0.0391-0.057 M/CMM

Imm Retic Frac

14.9

2.3-15.9 %

Ret-Hgb

24.6

L

30-35 PG

Reticulocyte counts are the quantity of the youngest red blood cells released from the bone marrow into the peripheral blood. Reticulocytes are reported as a % and the absolute reticulocyte count is calculated by multiplying the Retic% by the RBC. The immature reticulocyte fraction (IRF) is the rate of production of reticulocytes and depends largely on the ability of the bone marrow to respond to erythropoietin. The reticulocyte hemoglobin (Ret-He) content is the amount of hemoglobin in newly formed red blood cells. (There are two different hematology systems that report reticulocyte hemoglobin content. The two nomenclatures used for reticulocyte hemoglobin are Ret-He and CHr and studies have been done that demonstrate their equivalence)

Note that the Ret-He reflects the quality of the newly formed reticulocytes. Ret-He is a direct measurement of the amount of hemoglobin in each reticulocyte, which indicates the amount of iron available for incorporation into the precursors of mature red cells. This patient’s retic% and IRF are within normal ranges, but her absolute reticulocyte count is high. A Ret-He less than 29 pg in an adult is indicative of iron deficiency. With a normal CBC and low Ret-He, this is an early indication that iron deficiency is indeed present. With the absence of sufficient iron, this patient would eventually develop a microcytic, hypochromic anemia. Therefore, Ret-He can measure and indicate inadequate hemoglobin production before the hemoglobin and hematocrit decrease.

In this case the importance of clinical awareness is illustrated. This physician remembered a recent laboratory technical bulletin announcing implementation of a new hematology analyzer system with the availability of new parameters for reticulocyte counts. When the CBC results came back from the laboratory, the patient had already gone home, and no serum had been drawn to perform a ferritin level. Rather than calling the patient back to have another sample drawn, the Ret-He could be done from the same blood sample already in the lab. Ret-He is a faster, easier and less expensive test than additional iron studies and bone marrow iron stains. Ret-He can easily be used at a very low cost to get that first piece of information to decide whether or not iron deficiency is a concern. A high or normal Ret-He would have ruled out an iron deficiency with a fairly high confidence level. In this case, the low Ret-He could be used to guide further workups. A subsequent blood drawn revealed a low ferritin and iron deficiency was confirmed. The patient was advised to take an iron supplement along with ongoing treatment for the bleeding.

This case is just one example of the clinical utility of the Ret-He. Using the Ret-He, physicians can determine iron deficiency before iron deficiency IDA develops. A low Ret-He can alert a physician to iron deficiency without the presence of anemia, microcytosis or hypochromia. Ret-He can also be used to monitor and show early response to iron therapy before any other parameters change. A case example is that of a 5 month old who was brought to the emergency room with a Hgb of 7 g/dl and a Ret-He of 11.9 pg. In pediatric patients, a Ret-He less than 27.5 is an indicator of IDA. In this child, treatment with oral iron showed that the Ret-He had risen to 24.6 pg seven days after the onset of iron therapy, while the CBC remained virtually the same. This provided a very early indication that the iron therapy was effective.1 The Ret-He can also been used to minimize transfusions. The AABB Choosing Wisely Campaign lists 5 things that physicians and patients should questions before transfusion. One of the guidelines states “Don’t transfuse red blood cells for iron deficiency without hemodynamic instability.“2 Historically, physicians have used a ‘wait and see’ approach and watched Hgb levels drop before they start looking at iron. Using a Ret-He, iron deficiency could be determined, for example, in a patient with a Hgb of 11 g/dl. Oral or intravenous iron could be started before the Hgb drops below 7 g/dl and transfusion becomes necessary. The AABB Choosing Wisely Campaign emphasizes this by stating that patients with chronic iron deficiency or pre-operative patients with iron deficiency should be given iron therapy before transfusion is considered.2 Ret-He can give the earliest indication of iron deficiency and can be used to monitor the response to iron therapy. Another clinical utility of Ret-He has been to help diagnose or rule out iron deficiency in oncology patients. Additionally, Ret-He has been included in guidelines for anemia management in end stage renal disease patients on dialysis and who get erythropoietin.

The Ret-He parameter has proved clinically useful in early determination of functional iron deficiency. Traditionally ordered chemistry iron studies are indirect measures that have certain inherent inaccuracies due to the presence of inflammation and infection, or in patients on iron therapy. Ret-He is a direct and very effective screening tool and physicians can use Ret-He with other RBC indicies to improve anemia diagnosis and management in many patient populations. Ret-He can be used as a screening measure, and used to reflex for iron studies. Therefore, laboratories who have instruments that can report Ret-He and CHr should develop an education program to help clinicians effectively use Ret-He. Together physicians and laboratorians can develop their own guidelines for reflex testing and improvement for patient care.

-Becky Socha, MS, MLS(ASCP)CM BB CM graduated from Merrimack College in N. Andover, Massachusetts with a BS in Medical Technology and completed her MS in Clinical Laboratory Sciences at the University of Massachusetts, Lowell. She has worked as a Medical Technologist for over 30 years. She’s worked in all areas of the clinical laboratory, but has a special interest in Hematology and Blood Banking. When she’s not busy being a mad scientist, she can be found outside riding her bicycle.